This invention relates to novel 4-methylene-1,3-dioxolanes having functional groups, which is easy applicable to UV curable inks, coatings as a reactive thinner or a crosslinking agent, to a process for the production thereof and to the intermediates used in this process.
Commercially available vinyl ethers are based on base-catalysed addition of acetylene onto alcohols under pressure. The resultant compounds contain the structural element H2Cxe2x95x90CHxe2x80x94OR and have been used industrially for many years. These compounds have attracted particular attention in cationic and photocationic polymerisation as, due to their electron-rich double bond, they are generally highly reactive compounds.
However, users always complain that volatile, strong-smelling components are formed during crosslinking which, at elevated concentration, are irritant and thus problematic on occupational hygiene grounds. Comprehensive precautions are thus required on occupational safety and health protection grounds which not only entail considerable costs for users, but also put up the prices of their products.
It has been known for some time that one of the principal components of these unwanted volatile secondary products is acetaldehyde, which is produced in a secondary reaction of vinyl ether with ambient moisture. T. Moriguchi et al., Macromolecules 1995, 28, 4334-4339, have reported a possible reaction pathway.
Various approaches to solving this problem have been discussed for some time. From an economic standpoint, the most promising approach would seem to be to rearrange readily available allyl ethers to yield isopropenyl ethers on noble metal catalysts (J. V. Crivello, U.S. Pat. No. 5,486,545, Jan. 23, 1996). However, this approach overlooks the fact that, during cationic and photocationic polymerisation, isopropenyl ethers may also enter into a secondary reaction with water, analogous to that of the commercial vinyl ethers, resulting in the formation of propionaldehyde. Isopropenyl ethers are thus also incapable of satisfying the requirement for emission-free crosslinking. Open-chain vinyl ethers are in principle incapable of achieving this as it is always possible for them to give rise to volatile cleavage products in the presence of moisture.
Cyclic vinyl ethers, on the other hand, such as for example 2,3-dihydrofurans and 2,3-dihydropyrans, are virtually ideal vinyl ethers. While they may indeed also enter into secondary reactions with water during photocationic reactions, no volatile cleavage products are formed, as the irritant aldehyde component remains firmly attached to the molecule. However, these heterocyclic compounds, if they are to have a suitable degree of substitution which permits further conversion, are complex to synthesise, such that relatively large quantities have not hitherto been industrially available at reasonable cost.
In contrast, the class of 4-methylene-1,3-dioxolanes is much more straightforwardly available.
U.S. Pat. No. 2,445,733, Jul. 21, 1945, describes the first attempts to crosslink 4-methylene-1,3-dioxolanes. However, depending upon the metal ion, the Friedel-Crafts catalysts which are used give rise to reddish-brown coloured masses, but not to solvent-resistant networks. Using an alcoholic solution of zinc chloride (H. Orth, Angew. Chem. 1952, 64, 544-553) brought about some improvement, but the polymerisations performed were markedly exothermic and sometimes proceeded explosively on addition of the catalyst. One positive feature which may be noted, however, is that the resultant networks have considerable surface hardness and, consequently, good workability.
It has recently been found that 4-methylene-1,3-dioxolanes are also photocationically active. K. D. Belfield and F. B. Abdelrazzaq, Macromolecules 1997, 30, 6985-88 accordingly describe photocationic crosslinking of 2,2xe2x80x2-(1,4-phenylene)bis(4-methylene-1,3-dioxolane) with 2-phenyl-4-methylene-1,3-dioxolane. Both monomers are, however, of an aromatic nature, i.e. they have aromatic substituents in position 2. It is, however, now known that 4-methylene-1,3-dioxolanes which have a 2,2-diphenyl- or 2-phenyl-2-alkyl substitution polymerise with elimination of the ketone component (R. S. Davidson, G. J. Howgate, J. Photochem. Photobiol. A., 1997, 109, 185-193 and Y. Hiraguri, T. Endo, J. Polym. Sci. Part A: Polym. Chem. 1989, 27, 4403-4411), i.e. eliminating components of a greater or lesser degree of volatility. As a result, the requirement for emission-free crosslinking cannot be met.
It has now surprisingly been found that purely aliphatically substituted 4-methylene-1,3-dioxolanes differ fundamentally from the aromatic derivatives thereof and may be crosslinked under photocationic conditions without emissions. This is confirmed by findings in the scientific literature: 2-isopropenyl-4-methylene-1,3-dioxolane yields a linear polymer having ketone groups, wherein polymerisation proceeds exclusively by ring-opening (J. Park, N. Kihara, T. Ikeda, T. Endo, J. Polym. Sci. Part A: Polym. Chem. 1993, 31, 1083-1085).
The possibility of designing crosslinking systems based on 4-methylene-1,3-dioxolanes has hitherto more or less been restricted to the industrial availability of dialdehydes and diketones and the tetraacetals and tetraketals thereof. The lack of suitably substituted 4-methylene-1,3-dioxolanes is thus noticeably restricting the potential possibilities of this class of monomers.
The object of the invention is to provide novel 4-methylene-1,3-dioxolanes which have at least one further functional group, such as for example an OH group or ester group, such that further conversions are individually possible. These 4-methylene-1,3-dioxolanes should satisfy the following requirements:
(i) no elimination of acetaldehyde or propionaldehyde during crosslinking,
(ii) ready availability by means of industrially straightforward operations,
(iii) production from low cost basic substances available in industrial quantities,
(iv) no use of costly noble metal catalysts or catalyst systems which are difficult to regenerate,
(v) activity equal to or greater than commercial vinyl ethers,
(vi) low vapour pressure so that there is virtually no odour nuisance.
The present invention provides 4-methylene-1,3-dioxolanes of the general formula I 
in which R1 denotes hydrogen or alkyl, X denotes a single bond, C1-C18 alkylene, cycloalkylene, arylalkylene, xe2x80x94CH2(OCH2CH2)nxe2x80x94 or xe2x80x94CH2(OCH(CH3)CH2)nxe2x80x94, in which n is an integer from 1 to 100, and Z means a functional group selected from among xe2x80x94OH, xe2x80x94COORxe2x80x2 or xe2x80x94OCORxe2x80x2, in which Rxe2x80x2 denotes hydrogen or C1-C8 alkyl.
The 4-methylene-1,3-dioxolanes according to the invention, which may be considered 1,1-disubstituted vinyl ethers, satisfy the above stated conditions (i) to (vi). The reactivity of vinyl ethers is known approximately to follow the series R1R2Cxe2x95x90CHxe2x80x94Oxe2x80x94R less than R1CHxe2x95x90CHxe2x80x94Oxe2x80x94R less than CH2xe2x95x90CHxe2x80x94Oxe2x80x94R less than CH2xe2x95x90CR3xe2x80x94Oxe2x80x94R, i.e. the 1,1-disubstituted vinyl ethers are generally the most reactive if their substituents are not too sterically demanding (O. Nuyken, R. B. Raether, C. E. Spindler, Macromol. Chem. Phys. 1988, 199, 191-196).
The invention is based on the surprising observation that, despite simultaneously having an allyl structure (allyl compounds being known to have a slight tendency to polymerise), the 4-methylene-1,3-dioxolanes represented by the general formula I exhibit the elevated reactivity of 1,1-disubstituted vinyl ethers in photocationic reactions.
There follow some definitions of terms which are used in this document:
Unless otherwise stated, the term xe2x80x9calkylxe2x80x9d denotes a monovalent alkane residue of the general formula CnH2n+1, in which n denotes the number of carbon atoms and ranges from 1 to 18, preferably from 1 to 6.
The alkyl residues may be linear or branched.
Examples of such alkyl residues are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t.-butyl etc . . .
The term xe2x80x9calkylenexe2x80x9d denotes a linear or branched, divalent hydrocarbon residue having 1 to 18 carbon atoms.
Examples of such alkylene residues are methylene, ethylene, n-propylene, isopropylene etc . . .
The term xe2x80x9ccycloalkylenexe2x80x9d designates a cyclic alkylene residue having 5 or 6 carbon atoms.
Examples of such cyclic alkylene residues are cyclopentanediyl and cyclohexanediyl.
The term xe2x80x9carylalkylenexe2x80x9d denotes a divalent arylaliphatic residue, in which aryl denotes an aromatic hydrocarbon residue, for example phenyl, naphthyl or anthryl, and alkylene is defined as above.
According to a preferred embodiment of the 4-methylene-1,3-dioxolanes according to the invention, the functional group Z denotes an OH group or an ester group.
Particularly preferred 4-methylene-1,3-dioxolanes according to the invention are 2-methyl-2-hydroxymethyl-4-methylene-1,3-dioxolane, 2-(1-hydroxymethyl-2-methyl-propan-2-yl)-4-methylene-1,3-dioxolane, 2-methyl-2-ethoxycarbonylmethyl-4-methylene-1,3-dioxolane, 2-methyl-2-(1-cyclopentenylcarboxylic acid ethyl ester-1-yl)-4-methylene-1,3-dioxolane and 2-methyl-2-(propionic acid ethyl ester-3-yl)-4-methylene-1,3-dioxolane.
The 4-methylene-1,3-dioxolanes according to the invention are produced by a process which is characterised in that 4-chloromethyl-1,3-dioxolanes of the general formula II 
in which R1, X and Z are defined as above, are treated with a base at a temperature of 0xc2x0 C. to 150xc2x0 C. and the reaction product is isolated using per se known methods.
The process is preferably performed at a temperature of 20xc2x0 C. to 60xc2x0 C.
Suitable bases are alkali metal and alkaline earth metal hydroxides, such as for example sodium hydroxide, potassium hydroxide or calcium hydroxide, as well as the alkali metal salts of primary, secondary and tertiary alcohols, such as for example sodium methylate, sodium ethylate or potassium tert.-butylate. When such substances are not commercially available, the corresponding alkali metals, alkali metal hydrides or alkali metal hydroxides may be dissolved in the corresponding alcohols. Potassium tert.-butylate is particularly preferred as the base.
Treatment with a base may proceed without a solvent. Generally, however, it is more advantageous to use a solvent. These may be alcohols, such as for example methanol, ethanol, isopropanol, 1-butanol or tert.-butanol, as well as ethers, such as for example dioxane, ethylene glycol dimethyl ether or tetrahydrofuran, but solvents such as dimethyl sulfoxide or DMF are also suitable. Esters of any kind are, however, less suitable as they may saponify under the reaction conditions. Particularly preferred solvents are those which are good solvents for the base used, but do not dissolve the metal chloride formed during the reaction. In this manner, isolation of the product is simplified.
The invention also provides the chloromethyl compounds of the general formula II used for the production of the 4-methylene-1,3-dioxolanes according to the invention 
in which R1, X and Z are defined as above.
Preferred chloromethyl compounds of the formula II are 2-methyl-2-hydroxymethyl-4-chloromethyl-1,3-dioxolane, 2-(1-hydroxymethyl-2-methylpropan-2-yl)-4-chloromethyl-1,3-dioxolane, 2,4-bis(chloromethyl)-2-methyl-1,3-dioxolane, 2-methyl-2-ethoxycarbonylmethyl-4-chloromethyl-1,3-dioxolane, 2-methyl-2-(1-cyclopentenylcarboxylic acid ethyl ester-1-yl)-4-chloromethyl-1,3-dioxolane, 2,4-bis(chloromethyl)-1,3-dioxolane and 2-methyl-2-(propionic acid ethyl ester-3-yl)-4-chloromethyl-1,3-dioxolane.
The chloromethyl compounds II are simply obtainable by reacting functional aldehydes and ketones of the general structure III 
in which R1, X and Z are defined as above, with 3-chloro-1,2-propanediol. This reaction is catalysed by acids, such as for example p-toluenesulfonic acid or sulfuric acid. In the case of some reactive aldehydes, catalysis may be entirely dispensed with. Examples of compound III which may be mentioned are: hydroxyacetone, 2,2-dimethyl-3-hydroxypropanal, 3-acetyl-1-propanol, 1-hydroxy-2-methyl-3-butanone, p-hydroxybenzylacetone,, chloroacetone, glyoxylic acid, pyruvic acid, acetoacetic ester and very particularly 3,3-dialkyl-substituted acetoacetic ester, laevulinic acid, bromo- or chloroacetaldehyde dimethyl acetal.
The water arising during the reaction is removed by distillation, wherein the presence of a suitable entraining agent has an advantageous effect. Water-immiscible solvents, such as for example toluene, chloroform or cyclohexane are very particularly suitable for this purpose. It is immaterial whether the reagents dissolve homogeneously in the entraining agent or whether they form two phases. If no entraining agent is used, it is advisable to apply a slightly reduced pressure when removing the water, provided that the reagents used permit this. If a diacetal is used as the starting material, the resultant alcohol may readily be removed by distillation.
The functional 4-methylene-1,3-dioxolanes produced according to the invention, very particularly the compounds having OH and ester groups, may subsequently be converted, for example using suitable diols and diesters, into bis- and poly(4-methylene-1,3-dioxolanes) which are suitable as crosslinking agents in, for example, photocationic polymerisation systems.
The following practical examples illustrate the invention is greater detail: